Image-Guided Adaptive Therapy for the Treatment of Lung Cancer

C Ramsey, S Mahan, D Chase

Thompson Cancer Survival Center, Knoxville,TN

Adaptive IGRT for Lung

• The first Lung Cancer patient was treated with Helical Tomotherapy at the Thompson Cancer Center in July 2003

• 7 lung cancer patients have been treated for a total of 199 fractions

• Each patient had CT imaging prior to treatment delivery

Lung Window Bone Window

TCSC-RT 0301: Lung Tomo Protocol

Prescription• Initial: 44 Gy (2.0 Gy/fraction)• Boost: 20 Gy (2.5 Gy/fraction)

Margins• Initial: GTV + 2-cm• Boost: GTV + 1-cm (with DIBH)

Plan Optimization Parameters:• Pitch: 0.333• Thickness: 2.5• Modulation: 2.5

The total lung volume (right and left lung minus the gross tumor volume) receiving greater than

20 Gy must be 35% or less

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Lung Adaptive Therapy

TomoImage Fraction #1

TomoImage Fraction #30

GTV

GTV

Tumor Response •During the course of the therapy

(with or without concurrent chemotherapy), the GTV can reduce in volume by a factor of 3

•As the GTV shrinks, the target is effectively being treated with an increasing margin

Lung Adaptive Therapy

•The PTV is reduced every five fractions based on GTV volume reduction in the previous five TomoImages

•The GTV is reduced in the planning CT image to match each weeks measured tumor volume

•The GTV is still expanded into the PTV (i.e. margins are the same)

•Adaptive therapy’s impact increases the larger the original GTV volume and the greater the tumor response

Original Treatment Plan

Adaptive Composite Plan

Lung Adaptive Therapy

Non-Adaptive Weekly Adaptive

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Lung mass reduced to 36% of the original tumor volume

PTVIps. Lung

Lung Adaptive Therapy

Non-Adaptive Weekly Adaptive

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Lung mass reduced to 25% of the original tumor volume

PTV

Ips. Lung

Lung Adaptive Therapy

PTV

Ips. Lung

Weekly Adaptive Non-Adaptive

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Lung mass reduced to 81% of the original tumor volume

Adaptive IGRT for Lung

Based on the results of this feasibility study, adaptive therapy at a minimum has the potential to decrease radiation induced damage to healthy lung tissue

• The level of improvement increases with larger initial CTV’s and with increased volume reduction during treatment

The potential pitfall of this type of adaptive therapy is the potential for underdosing microscopic extension

• As the visible GTV decreases, the assumption is that the microscopic extension is also shrinking at the same rate

• However, margin is still added around the GTV in adaptive therapy, and the final PTV is typically the same size or larger than the initial CTV